The present invention relates generally to the calibration of spectrophotometric instruments. In particular, the invention is a probe, calibration structure and algorithm for calibration of spectrophotometric instruments.
Spectrophotometric-type instruments are known and used in a variety of applications. An instrument of this type is, for example, disclosed in the Anderson et al. U.S. Pat. No. 5,879,294. Instruments of this type include an optical probe which is releasably connected to an electronics package. In operation, the probe is positioned on the tissue to be measured or analyzed. The probe is interfaced to the instrument electronics through optical fibers and a probe connector. Light used to measure the characteristics of the tissue is coupled to the probe by send optical fibers. After being transmitted from the tissue-engaging surface of the probe into the tissue being measured, the light will travel through the tissue before being collected at the end of a receive optical fiber. This collected light is then transmitted to the instrument through the probe connector and electronics package connector.
The collected measurement light signals received by the electronics package are transmitted to a detector which produces electrical signals representative of these light signals at each wavelength of interest. A processor/controller then processes these signals to generate data representative of the measured tissue parameter. The measurement can be visually displayed on a display. Algorithms used to compute the tissue parameter data are generally known and described in the Anderson et al. patent.
Calibration procedures are typically performed to enhance the accuracy of the measurements made by the instrument. Methods and devices for calibrating spectrophotometric-type instruments are generally known and disclosed in the Anderson et al. patent. The calibration can, for example, be performed by placing the probe on a calibration device having a housing which is filled with light scattering material. The light scattering material is generally spectrally flat (i.e., reflects all light to the same degree) to provide a reference spectrum. White polyethylene foam such as Plastazote LD45 available from Zotefoams plc. can be used for this purpose.
To obtain an accurate calibration it is important that the-probe be properly positioned on the calibration device during the reference measurement. Inaccurate calibrations will occur when the probe is positioned on the tissue of a patient or otherwise positioned in a manner which enables ambient or other light besides that of the send optical fibers to reach the receive fiber.
There remains a continuing need for improved calibration devices and methods for use with spectrophotometric instruments. Devices and methods which are convenient to use would be especially desirable. Any such devices and methods must be capable of providing accurate calibration procedures.
The present invention is an instrument, probe and calibration device for conveniently and accurately calibrating a spectrophotometric instrument. One embodiment of the instrument includes light signal sources, a detector, a processor/controller, a probe and a calibration device. The light signal sources include a source of measurement light signals having measurement light wavelengths and a source of a calibration light signal at a calibration detection wavelength which is different than the measurement light wavelengths. The probe has one or more send fibers coupled to the measurement and calibration light signal sources for transmitting the measurement light signals and the calibration light signal into tissue, and one or more receive fibers for receiving light including the measurement light signals and the calibration light signal. The calibration device is adapted to receive the probe and has an optical filter for transmitting the measurement light signals but not the calibration light signal. The detector is coupled to the receive fibers to generate electrical signals representative of the light received at the receive fibers. The processor/controller is coupled to the detector and initiates a calibration procedure when the calibration light signal is not detected.